1. Field of the Invention
The present invention relates to a zoom lens system. Moreover, the present invention relates to an image pickup apparatus including a video camera and a digital camera.
2. Description of the Related Art
In recent years, replacing a camera in which, a film is used, a digital camera in which, an object is photographed by using an image pickup element such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor) sensor has become mainstream.
Furthermore, there are several categories of digital cameras in a wide range from a high-function type for professional use to a compact popular type.
From among these categories, a user of a digital camera of the popular type seeks to enjoy photography by capturing readily various scenes at any time and anywhere. Therefore, a digital camera having a small size, and which can be carried conveniently is preferred.
For carrying out slimming and small-sizing, an image pickup element is to be made small. Here, in an image pickup element which is small-size, for letting the number of pixels to be same as the number of pixels of the image pickup element before small-sizing, it is necessary to make a pitch of pixels small. Therefore, in the image pickup element which is small-size, insufficiency of sensitivity has to be covered by an optical system. Consequently, an optical system having a bright F value is necessary.
Whereas, a zooming ratio of about three times and an angle of field at a wide angle end of about 63° of a zoom lens system which is used in a digital camera of a compact type, are common.
As such optical system, an optical system which includes in order from an object side, a first lens unit having a positive refracting power, a second lens unit having a negative refracting power, a third lens unit having a positive refracting power, and a fourth lens unit having a positive refracting power, and in which, distances between the lens units change at the time of zooming from a wide angle end to a telephoto end, has been known. An example of a conventional technology of such optical system is disclosed in Japanese Patent Application Laid-open Publication Nos. 2004-252204, 2003-315676, and 2001-242379.
A zoom lens system disclosed in Japanese Patent Application Laid-open Publication No. 2004-252204 is a zoom lens system in which, the F value is about 2.8 at the wide angle end, the zooming ratio is about three, and the angle of field at the wide angle end is about 63°.
A zoom lens system disclosed in Japanese Patent Application Laid-open Publication No. 2003-315676 is a zoom lens system in which, the zooming ratio of four and more has been secured, but the F value is about 2.8 at the wide angle end, and the angle of field at the wide angle end is about 63°.
A zoom lens system disclosed in Japanese Patent Application Laid-open Publication No. 2001-242279, is a comparatively bright zoom lens system having the F value of about 2.0 at the wide angle end, but is a zoom lens system having the zooming ratio of about three, and the angle of field at the wide angle end of about 63°.